Selenium is a trace mineral found in soil, water and some foods. It is required for the body to function normally, but only in small amounts. Selenium boosts the performance of enzymes, which help the body carry out many chemical reactions that are crucial for brain and body functions.

Selenium appears to provide many health benefits to the body. It may help prevent the development of illnesses such as heart disease and cancer, aids in regulating the function of the thyroid gland, and helps strengthen the immune system.

Several foods are naturally rich in selenium. The best sources of selenium include dairy products, meats (especially organ meats such as liver and kidney), seafood and certain nuts. In addition, selenium is present in grains, seeds, fruits and vegetables grown in selenium-rich soils.

Selenium deficiency is rare in the United States and Canada. However, when selenium deficiency does occur, it can lead to heart disease, hypothyroidism (low production of thyroid hormone) and a weakened immune system. In particular, selenium deficiency can lead to Keshan disease, in which the heart becomes enlarged and fibrous tissue replaces the muscle tissue in the middle layer of the heart’s walls.

Experts advise adults not to consume more than 400 micrograms of selenium in a single day. Long term consumption of excessive selenium can lead to a condition called selenosis and symptoms such as fatigue, garlic odor on the breath, and loss and brittleness of hair and nails.